Experimental and numerical study on the effects of embedded cylindrical sensors on the interlaminar shear behavior of unidirectional composite laminates

Abstract

Integrating self-sensing ability into structural materials has widespread applications which include temperature measurement of composite parts and repair patches with embedded wireless temperature sensors. The parasitic effects of the embedded sensors on the structural integrity need to be investigated. Interlaminar shear failure is one of the critical failure modes for laminated composites. The effect of embedding a cylindrical microwire temperature sensor on the interlaminar shear strength of laminates fabricated from an Out-of-Autoclave material was investigated. The fact that an 'eye-shaped' resin rich region formed, when the sensors are placed orthogonal to the fiber direction, was taken into account. The sensor-laminate configurations included sensor placed at the mid-plane, one ply above mid-plane and two plies above mid-plane. Experiments were carried out using a three-point test setup. There was no significant strength reduction observed with the three configurations. Digital Image Correlation technique was used to measure through-thickness shear strains at various load levels. Two-dimensional plane stress finite element models were used to understand the mechanisms in the presence of embedded sensors. Progressive failure analysis was used to predict material failure. Experimentally generated surface strains and numerically computed surface strains were compared for each configuration. It was observed that the experimental and the numerical strains only agreed up to the elastic limit of the material. Also, due to the stress concentrations induced in the vicinity of the embedded sensor, the shear stress state no longer agreed with the classical beam theory.